Unfortunately that chronograph method is not safe with surplus bulk powders. They vary enough to act like significantly faster or slower powders on a powder chart would do. It's therefore possible to go well above healthy peak pressures with a new lot number when trying to match your previous lot's velocity. This is one reason for powder lot rejection by the military: when that lot can't reach their velocity window inside their pressure window. There's a good description by a former Aberdeen Proving Grounds Test Director in post 25, here.